Full Geo Trio with any two of the following can do the work: Slave 1, Vader, Silencer.
BH Quartet with Vader or Silencer also works.
Also, note that the zeta challenge itself doesn't require dark side ships. You can use light side stuff all you want. However, the five star executrix challenge, the completion of which is required, needs 5 dark side ships.
For that executrix challenge you'll be facing rebels. So I strongly suggest farming that new TIE Bomber, as it's built to destroy rebel scum. Best rebel counter ever.
Preferred gear level is 6 star, gear 8.
Kylo unmasked doesn't solo anyone as long as that team has an attacker or healing immunity or shock. He can force low offense teams like Phoenix to a timeout though given gear advantage though. Most of the time he'll die in 30 seconds if someone attempted to solo teams with him.